To expect parents in mid '70's to host Christmas with very young children?

You sound like you really dislike your sister?

This. @Birminghamx seems very judgmental of her sister’s choices. Not everyone is lucky enough to find a life partner.

And it IS luck, not that the OP and her brother are superior people (although she seems to think so).

You seem to resent your sister. And you are very judgemental of her. Were your DC perfectly behaved at 5 months old?

Your parents are trying to help her. They may understand why she made the choice to be a parent without a partner better than you do.

Yes it’s difficult to see siblings appear to exploit parents, but your sister has her own relationship with your parents which you can’t control. Maybe you could help your parents instead of bitching about your sister?

This saves me writing what I would have added OP but I hope it all works out for everyone.

So this year you’ll both have parents in law.
But you still think your sister shouldn’t go to your mums can you see how logical that sounds?

This works for you and your brother but it doesn’t work for your sister, she doesn’t have the space to accommodate your parents so she misses out on Christmas with her family whilst you and your brother get to spend family christmases with your parents every other year.

Equally your parents miss out on time with their daughter (however difficult) and their grand daughters.

However hard it is, you need to stay out of the solution they have come up with.

Why yours?

You know that this is absolutely none of your business. Your parents are capable of making decisions for themselves. You have a third party narrative that your mum was tired for a couple of days. I would always sacrifice a couple of days if it meant not leaving my daughter alone on Christmas Day with two small children.

It's really important that you stay out of this. Your relationship with your parents is completely separate from her relationship with her parents. You can not go on thinking you need to rescue your parents from your sister.

But not your sister 🤔

I'm just glad that my family don't treat me like this, being single by choice with children.

Honestly. let your parents spend Christmas with your sister. Sounds like they would rather that.

Yes, I wouldn't be at all surprised if the OP's parents can see what's going on more clearly than the OP, who seems to be in sibling-rivalry mode and isn't, on this issue, acting like a dispassionate adult.

It can be challenging having someone like OP's sister in the family. In my own experience, many a pleasant family event was marred by my sister's apparently unreasonable behaviour and yes, I used to be furious with her for being so difficult. She can still be infuriating, but now we understand what's going on and sometimes we can change things to ensure that it's easier for her to cope with. Perhaps that's why the OP's parents are happy to host DS and children — because they see the bigger picture and accept that that's how she is and offer what she needs.

I’m sure one of you can fit your sister in for Xmas, you just don’t want to. Hopefully you won’t be a single parent one day with no one wanting to invite you round at Xmas.

And?
Presumably you'll tell them that you won't be hosting again then?
It didn't have be expensive or exhausting hosting 2 other adults

@Birminghamx you sound selfish, jealous and controlling.

You still haven't answered if one of you will take your sister? Or do you want her and her children to spend Christmas alone?

You sound like a miserable person

If you had two kids though would you want one to not be included and on their own?

We hosted daughter and her boyfriend, are decades younger, and found it incredibly ( expensive) and stressful.

If I understand correctly, if it's you or your brother, your parents stay with you (so you must have the space to accommodate). When visiting your sister, they stay in a hotel because she doesn't (have space). But you denigrate your sister. Maybe think seriously about that is what I'd say.

No, no, no. If one of my daughters did this she would be shown the door.
Op is deliberately trying to exclude her sister from family Christmas celebrations when what happens in her parents house is none of her business.
Why do some people think that once we each pension age we cannot think or speak for ourselves?

I was just coming to say this, one has parents, the other hosts sis and kids. I know you have issues with her, after a post further down the thread, but for your parents sake, I think u should suck it up and do this, show some Christmas spirit. I’m sure sis would want to be with family rather than friends, especially as she’s got children. Your parents are going to feel terribly guilty knowing sis is on her own, if they aren’t at home to host her and they are with her sibling

This is the type of "I know what's best for them" scenario that causes rifts in families. You decide for everyone, but you don't actually offer to include everyone in your plans. Why don't you host for the whole family? If the response is going to be "not enough room", then why not host at your parents house? You do all the work, food, planning etc, and they put their feet up in their own home (and even catch a quick nap when/if things get too much for them). Stop telling other people what to do, and offer to help instead.

My understanding of it is that neither OP or her brother have invited their parents to either of theirs as they are hosting their in laws..

They are annoyed that their sister is going to their parents again this year (same as last year) and they think they should intervene to stop it somehow?

So since neither you nor your brother can host you sister over Christmas, and she cannot host you, you are proposing that your sister stays at home alone in her small flat whilst you, brother and parents have a very Merry Christmas?

With siblings like you, who needs enemies?

If both you and your brother can host your parents and in-laws at the same time, and your parents can only be in one place at a time, then whoever doesn't have your parents can have your sister?

Sorry for double posting, but maybe the reason your parents want it at their house, despite it being so much more work, is that when someone else hosts Christmas 1/3 of their family is excluded. The same predictable 1/3 every time.

I really hope they are wise to you.